📐 Sashing Layout Calculator

Enter your block grid (how many blocks across and down), block size, sashing strip width, and border width to calculate the total finished quilt size.

Blocks across

Blocks down

Block size (in)

Sashing width (in)

Border width (in)

Blocks, plus one more sashing strip than you might expect

width  = across × block + (across + 1) × sashing + 2 × border
height = down   × block + (down   + 1) × sashing + 2 × border

The defaults - a 4 × 5 grid of 6 in blocks, 2 in sashing, 3 in borders - give 24 + 10 + 6 = 40 in across and 30 + 12 + 6 = 48 in down. Note the across + 1: four blocks have three gaps, so the two extra strips exist only because sashing runs round the outside of the block field too.

If you do not want sashing on the outer edges

Then three strips run across, not five, and the tool is two sashing widths over in each direction:

Sashing	Width as calculated	Without outer sashing
1 in	35 in	33 in
1.5 in	37.5 in	34.5 in
2 in	40 in	36 in
3 in	45 in	39 in

Subtract twice the sashing width from each dimension if your sashing stops at the last block. Cornerstones change nothing - a pieced square at each junction occupies space the crossing strips already take.

Every number here is a finished measurement. To cut, add two seam allowances: 2 in sashing is cut 2.5 in wide, 6 in blocks are cut 6.5 in. Borders are usually cut long and trimmed after attaching, because a top rarely comes off the machine at the size the arithmetic promised.

Frequently asked questions

How do I calculate quilt size with sashing and borders?

Add the blocks in a row, the sashing strips between and around them, then twice the border. A 4 by 5 grid of 6 in blocks with 2 in sashing and 3 in borders finishes at 40 × 48 in.

How wide should sashing strips be?

The calculator takes whatever you choose, and the table shows what each costs in total size. Narrow sashing reads as a grid line; wide sashing turns the blocks into separate panels.

How much does sashing add to a quilt?

More than people expect, because it falls between every pair of blocks and again at the edges. Here 2 in sashing adds 10 in across and 12 in down, over 40 per cent on top of the 24 in of blocks.